A first target engine speed N1 and a high-speed control area F1 are set according to a command value commanded by a command unit. A second target engine speed N2 and a high-speed control area F2 defined on a low-speed side are set according to the first target engine speed N1. A pump displacement D and an engine torque T of a variable displacement hydraulic pump are detected so that a target engine speed N corresponding to each of the detected pump displacement and engine torque is detected according to a preset relationship between a the pump displacement D and the target engine speed N and a preset relationship between the engine torque T and the target engine speed N during an engine control at the high-speed control area F2. The drive of the engine is controlled so that the engine is driven at the target engine speed N.